Consider the composition of a Bitcoin block (what goes inside a block). Which of the following items are not chosen (or modified) by a miner who is competing for the right to form the next block (i.e., to solve the nonce)?

           I.         the hash output of the previous block

           II.         the order of transactions in the candidate block (i.e., Merkle tree of transactions)

           III.         time stamp of the block

           IV.         difficulty of task (how many zeros the hash output has to have)